Anaerobic digestion in the United Kingdom

Anaerobic digestion (AD) has been used to treat sewage sludge by the United Kingdom’s (UK) water industry for over 100 years. More recent years have seen a revolution as AD has swiftly expanded into agricultural feedstocks and food waste. Data from the Waste Resource and Action Programme (WRAP) shows that in the past year alone, there has been a 46 percent growth in the size of the sector. There are now 108 nonwater industry AD plants in the UK (April 2013) — up from 74 a year ago — with a further 169 projects having received planning permission. Another 146 AD plants are in the water industry according to Water UK.

The UK AD market is diverse with plants of a wide range of sizes, treating a variety of different feedstocks. Of the UK’s nonwater industry plants, 44 use agricultural feedstocks such as slurries and crops, 47 treat food waste from various sources including supermarkets and households, and 17 are based on industrial sites, treating on-site waste such as brewery effluent. Primarily because of the way the financial incentives regime developed, the vast majority of plants operating today are generating electricity through combined heat and power (CHP) engines, and making some use of the heat. However, the Renewable Heat Incentive was recently introduced, and the UK now has three biomethane to grid plants, including the first commercial scale plant launched by the Prince of Wales in Poundbury, Dorset, in 2012. The Renewable Heat Incentive offers financial support for 20 years for biomethane injected into the gas grid at all scales, as well as heat produced from biogas plants with a thermal capacity up to 200 kW.

To realize the real potential for AD to contribute to the circular economy — by making the best use of finite resources and recycling nutrients back into food production, energy and food security, climate change, air quality and the economy — there are still barriers that the industry must overcome. Anaerobic digestion’s multiple benefits can sometimes act as a handicap given the need for government policy to be joined up across policy areas as diverse as waste, bioenergy, transport and agriculture.

Key Challenges And Solutions

To address these issues and support ongoing development, the Anaerobic Digestion and Biogas Association (ADBA), has highlighted six key challenges and their solutions:

The Investment Risk: AD is still reliant on government incentives to attract finance, build confidence and achieve growth. Potential investors can be nervous about uncertainty over tariff levels and key policies in areas such as waste, transport and bioenergy. Stability will come from long-term support at sufficient levels to reflect the risks, with capacity triggers (e.g., the 200 kW limit in the Renewable Heat Incentive) set at sensible levels and a workable preaccreditation system across all incentive schemes. At present, for example, the preset levels of deployment, if reached, will trigger reduced Feed-in-Tariff levels in April 2014. There is concern this has been set at too low a level, which could therefore cause investor confidence to be damaged. A preliminary accreditation model, which locks in a tariff rate prior to a project’s completion, can help to tackle this uncertainty.

Access To Feedstock: Irrespective of financial stability, without feedstock there is no AD industry. The best way to increase the volume of material available for processing through AD would be to support source segregated collections of organic waste and consider implementing a ban on biodegradable material sent to landfill, as the Scottish Government has done. Crops for AD are also a significant potential feedstock, offering additional benefits to farming over and above energy production, and should be clearly supported. Climate change targets cannot be met without sustainably produced bioenergy, but just as importantly, our nation’s food security is dependent on recycling the valuable nutrients contained in the food waste and other organic feedstocks.

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